1. Technical Field
The technical field relates to an optical pickup device and an optical disk device mounted in an electronic apparatus, such as a personal computer or a notebook computer.
2. Description of the Related Art
As electronic apparatuses, such as personal computers and notebook computers, have become smaller, optical pickup devices and optical disk devices mounted therein have also become smaller.
FIG. 13 is a view illustrating the configuration of main parts in an optical system of a known optical pickup device. A light source 101 emits a laser beam for a Digital Versatile Disk or Digital Video Disk (hereafter: “DVD”) having a wavelength λ1 of about 650 nm and a laser beam for a compact disk (hereafter: “CD”) having a wavelength λ2 of about 780 nm toward an optical disk 104. A prism 102 is formed of optical glass, for example, and has a slope where a beam splitter 103 is formed inside the prism 102. The beam splitter 103 is formed by using a polarization separating film and has a property of transmitting a laser beam, which is emitted from the light source 101 and moves toward the optical disk 104, and of reflecting a laser beam reflected from the optical disk 104. The optical disk 104 is a DVD or a CD. The detection lens 105 is an astigmatism-generating element. Since the detection lens 105 has a shape of a so-called columnar lens or cylindrical lens, focal distances on two perpendicular cross sections including an optical axis are different. An optical receiver 106 has a light-detecting portion 107 which detects light reflected from the optical disk 104.
Light emitted from the light source 101 is transmitted through the beam splitter 103 and is then incident on the optical disk 104. Light reflected from the optical disk 104 is reflected by the beam splitter 103, is incident on the detection lens 105, and is then incident on the optical receiver 106.
FIG. 14A is an explanatory view illustrating a known detection lens, FIG. 14B is a view illustrating a state of a spot when an optical disk is near, and FIG. 14C is a view illustrating a state of a spot when an optical disk is far. Referring to FIG. 14A, light 108 transmitted through the detection lens 105 forms a focal point in the neighborhood of the optical receiver 106. A focal point 109 of the light 108 on a cross section in the vertical direction is positioned ahead of the optical receiver 106, and a focal point 110 of the light 108 on a cross section in the horizontal direction is positioned behind the optical receiver 106. That is, the optical receiver 106 is disposed between the two focal points 109 and 110. The shape of a spot 111 on the optical receiver 106 is almost circular.
As shown in FIG. 14B, in the case where the optical disk 104 is close to an optical pickup device, the spot 111 of a laser beam in the optical receiver 106 becomes long in the horizontal direction. On the other hand, as shown in FIG. 14C, in the case where the optical disk 104 is far from the optical pickup device, the spot 111 has a long shape in the vertical direction. A focus control signal can be obtained by disposing the A to D light-detecting portions 107 in a cross shape and calculating a focus error signal FES=(A+C)−(B+D). That is, since the focus error signal FES>0 in the case where the optical disk 104 is near and the focus error signal FES<0 in the case where the optical disk 104 is far, the position of the optical disk 104 can be checked.